Method of plastically forming splines on shaft-like workpiece

ABSTRACT

A method of plastically forming splines on a shaft-like workpiece is provided. The volume of part of the shaft-like workpiece on which the splines are plastically formed is generally the same as the volume of plastically processed portion following processing. In addition, the part on which the splines are formed first is made with a maximum diameter. The shaft-like workpiece extends from the first formed part toward the part that is not plastically processed in a conical shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Japanese Patent Application No. 2006-299877, which was filed on Nov. 6, 2006 and which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method of plastically processing splines on a shaft-like workpiece.

2. Description of the Related Art

Conventionally, frequency modulation has been used as a forming technique for plastically deformable materials. (see JP-B-3572544 and U.S. Pat. No. 6,212,929, which are hereby incorporated by reference). Frequency modulation is the superimposing of high-frequency oscillation on the feed movement during spline formation. This forming process makes it possible to obtain a finished product directly from a blank without requiring the removal of surplus material. This plastic forming process also reduces manufacturing cost, and generally eliminates the creation of shavings. Such a plastic forming process makes it possible to eliminate the step of deburring or removing surplus material, to a considerable extent, although not completely in reality.

When splines on a shaft-like workpiece of, for example, an outboard motor, such as that shown in FIG. 8, by plastic forming, the shaft-like workpiece 100 comprises a shape in which the fore-end 101 a of the portion 101 to be formed with splines has a flared shape in consideration of the reduction in diameter at the spline fore-end.

The fore-end 101 a of the portion 101 to be provided with splines is formed in the flared shape for plastic forming of the shaft-like workpiece 100 by frequency modulation as well as for roll forming of splines or serrations.

However, when the shaft-like workpiece 100 as a blank is processed, burrs 120 a develop as shown in FIG. 9 along the ridge portion 120 between adjacent splines 110.

SUMMARY OF THE INVENTION

Accordingly, certain features, aspects and advantages of an embodiment of the present invention have been made to address the imperfections commonly encountered when working materials to form splines. Thus, one feature, aspect or advantage of an embodiment of the present invention provides a method of plastically forming splines on a shaft-like workpiece that make it possible to reduce the development of burrs on part of the shaft-like workpiece on which splines are plastically processed and that makes it possible to reduce the likelihood that the large diameter at the fore-end of the splines will be reduced.

One aspect of an embodiment of the present invention involves a method of plastically forming splines on a shaft-like workpiece, wherein a volume of splines formed on the shaft-like workpiece is made substantially equal to a volume of a plastically processed portion. The method comprises preparing the shaft-like workpiece such that the shaft-like workpiece has a maximum diameter in a portion where spline formation will begin, and such that the shaft-like workpiece extends in a conical shape from the portion where spline formation will begin toward a portion that will not be plastically processed. The method also comprises loading the shaft-like workpiece onto a machine and forming the splines.

Another aspect of an embodiment of the present invention involves a shaft-like workpiece blank. The blank comprises a shaft portion and a working portion. The working portion comprises a distal end and a proximal end with the proximal end being closer to the shaft portion than the distal end. The working portion is adapted to receive splines by plastic deformation. The working portion comprises a distal outer diameter and a proximal outer diameter. The distal outer diameter is larger than the proximal outer diameter and an outer surface of the working portion tapers from the distal outer diameter to the proximal outer diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the present invention will now be described with reference to the drawings of a preferred embodiment, which embodiment is intended to illustrate and not to limit the invention.

FIG. 1 is a schematic view of a plastic forming machine used for form shaft splines.

FIG. 2 is a sectional view of a die used to form the shaft splines.

FIG. 3 is a side view of a shaft-like workpiece before being processed.

FIG. 4 is a side view of the shaft-like workpiece after being processed.

FIG. 5 is an enlarged view of the part between adjacent spline ridges.

FIG. 6 is a graphical comparison of feeding forces in two plastic processing processes.

FIG. 7 is a graphical evaluation of feeding forces.

FIG. 8 is a side view of a conventional shaft-like workpiece before processing.

FIG. 9 is a side view of the conventional shaft-like workpiece after processing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a machine 1 can be provided to plastically form shaft splines on a shaft-like workpiece 24 with the main part 2 of the machine 1 comprising a column 3 and a chuck 4. Tie bars 5, 6 are provided between the column 3 and the chuck 4. The tie bars 5, 6 are provided with a movable slider 15. A die holder 7 is attached to the slider 15. A die 8 is received in the die holder 7.

A first feeder 9 is provided on the column 3. A pressing cylinder 10 is used with the first feeder 9 to move the die 8 through the die holder 7 provided on the slider 15. A frequency modulator 11 built in the first feeder 9 performs the frequency modulation used during the plastic forming process.

The machine main part 2 has a column 20 to which a second feeder 21 is attached. A work inserting cylinder 22 is used with the second feeder 21. The shaft-like workpiece 24 is inserted into the work grip 23 of the work inserting cylinder 22. The work inserting cylinder 22 moves the shaft-like workpiece 24 toward the die 8 to create relative motion between the shaft-like workpiece 24 and the die 8, thereby plastically forming splines on the shaft-like workpiece 24.

Next, steps of plastically forming the shaft splines are described. First, the shaft-like workpiece 24 is inserted into and attached to the work grip 23. By the operation of the work inserting cylinder 22, the shaft-like workpiece 24 is moved through the work grip 23 into the chuck 4, and held with the chuck 4. The die holder 7 is moved forward with the pressing cylinder 10 while applying frequency modulation with the frequency modulator 11. At this time, the die 8 in the die holder 7 causes plastic deformation of the shaft-like workpiece 24 so that splines are plastically formed on the shaft-like workpiece 24.

After plastically forming the splines, the die holder 7 is retracted by the pressing cylinder 10. The chuck 4 is released, the shaft-like workpiece 24 is retracted by operation of the work inserting cylinder 22, and the shaft-like workpiece 24 having splines formed thereon is taken out of the work grip 23.

As shown in FIG. 2, the die 8 is held, via a sleeve 12, in the die holder 7, which can have a band of plural thin steel layers (not shown). The die holder 7 is provided with a processing oil passage 13.

To plastically form the splines, the shaft-like workpiece 24 as a blank is clamped, and the die 8 of a shape complementary to the desired spline is firmly pressed over the shaft-like workpiece 24. The geometry of the splines is dependent on the dimensions and shape of the die 8. Because the die 8 is held in an interference fit in the die holder 7, the geometry of the die 8 is determined based upon the mounted state. The die 8 preferably is made of a superalloy or cemented carbide. Thus, a spline profile, once formed, generally cannot be changed. Accordingly, the die 8 preferably is held within the die holder 7 by the sleeve 12 and the thin steel band, which can define a metallic spring, so that the longitudinal direction of the die 8 may be adjusted by steps of for example 0.5 mm. Such a construction makes the over pin diameter of the shaft-like workpiece 24 adjustable within a range of up to about 0.1 mm.

The shaft-like workpiece 24, as shown in FIG. 3, preferably comprises a portion 24 a where splines are to be plastically formed. The effective length of the spline is L2. The spline part of the effective length of L2 can be coupled with a mating member, when mounted for final use, to transmit power. The diameter D2 at the fore-end 24 c preferably is greater than the diameter d2 of the root 24 b of the effective length L2 of the spline. Thus, the spline part can be formed in a conical shape with a straight slope surface 24 d of a specified angle of θ2 extending from the root 24 b to the fore-end 24 c.

Dimensions of the part 24 a of the illustrated shaft-like workpiece 24 can be: diameter D2 of fore-end 24 c: 21.02 mm; diameter d2 of root portion: 20.145 mm; spline effective length L2=9.688 mm>spline effective length of 7.8 mm; and specified angle θ2=2.747 degrees. The specified angle θ2, therefore, can be between about 2 degrees and 3 degrees in one configuration, but other angles also can be used. The volume of the splines formed on the shaft-like workpiece 24 preferably is about the same as the volume of the preprocessed shaft-like workpiece and the shaft-like workpiece preferably has a maximum diameter at its tip end 24 c where the splines are formed first, and extends in a conical shape from the tip end 24 c toward a base portion 24 b that is not plastically processed.

Using the forming machine 1, as shown in FIG. 1 for plastically forming splines on a shaft, the splines 30 as shown in FIGS. 4 and 5 were plastically formed on the shaft-like workpiece 24 by frequency modulation.

Plastically forming the splines 30 is done by pressing the die 8 of a shape complementary to the splines firmly into the blank. Plastic processing by frequency modulation is done by pressing the die 8 into the blank or the shaft-like workpiece 24 while vibrating the die 8 back and forth at a certain frequency (optimized according to materials and specifications) or while giving frequency modulating motion to the die 8. In this process, the feeding force can be reduced by about half as shown in FIG. 6 in comparison with that of a continuous plastic forming process. Action energy is saved so that a smaller machine can be used to form a workpiece than would be possible with the continuous plastic forming process. During the back-and-forth vibration, processing oil can be supplied through the oil passage 13 to the forming point every time the die moves back. This reduces the likelihood of the die 8 sticking to the material or the shaft-like workpiece 24 due to heat. The small feeding force also reduces the likelihood of the material bending or deforming.

The plastic forming process by frequency modulation accomplishes a removal process ratio of one-tenth or less compared to using a hob within a remarkably short period of time. In comparison with a removal process using a hob, pitch error and cog profile error are improved by 1 to 3 in the precision class number according to the Japanese Industrial Standards.

The plastic processing oil used for materials that are difficult to process with plastic forming, such as stainless steel, can be a chlorine-based agent for ultra-high contact pressure. In one embodiment, however, a chlorine-free agent can be used while plastically forming the splines. Using the chlorine-free plastic processing oil made it possible, as shown in FIG. 7, to keep the pressing force constant to the end of plastic processing by frequency modulation and, moreover, the retraction force was minimized.

In the illustrated configuration, the shaft-like workpiece 24 was made of low-carbon alloy steel, cold-forged in the shape shown in FIG. 3, and deburred. The material was formed so that the volume of the formed splines would be the same as the volume of the part plastically processed by frequency modulation. Further, the fore-end part 24 c, where the splines 30 are first formed, is made in a maximum diameter. From there, the fore-end part 24 c extends in a conical shape toward the root 24 b to which no plastic processing by frequency modulation is applied. When no inflection point is present in an area to which the plastic processing by frequency modulation is applied, it is possible as shown in FIGS. 4 and 5 to be free from burrs on the spline ridges 31. In other words, there preferably is no location along the portion that will be plastically deformed at which the diameter is smaller than a diameter toward the root of that portion.

As described above, the shaft-like workpiece 24 has no inflection point. Therefore, burrs are restricted from developing and the large diameter at the fore-end of the splines is not likely to decrease. As the finished product is obtained directly from the blank, the step of removing extra material is unnecessary, so that manufacturing cost can be reduced.

This above-described embodiment is described as an application in which the splines 30 are plastically formed on the shaft-like workpiece 24 using frequency modulation. However, certain features, aspects and advantages of the present invention also may be useful with plastic forming processes not using frequency modulation. While the shaft-like workpiece 24 is used for power transmission in outboard motors, the use is not limited to that but may be used also for power transmission in vehicles.

In outboard motors, two shafts are used to transmit power from the engine or prime mover to the propeller or propelling part. One is the drive shaft extending downward from the rear end of the crankshaft, which is disposed generally vertically during use, and the other is the propeller shaft, which is connected at right angles to the drive shaft through a set of gears. Each of these shafts has splines at one or more of its ends.

Certain features, aspects and advantages of the present invention may be applied to the method of forming splines on a shaft-like workpiece by plastic forming. When so used, at least a portion of the shaft-like workpiece, on which the splines are plastically formed, is restricted from developing burrs. The large diameter portion at the fore-end of the splines also is less likely to be reduced in diameter.

Although the present invention has been described in terms of a certain embodiment, other embodiments apparent to those of ordinary skill in the art also are within the scope of this invention. Thus, various changes and modifications may be made without departing from the spirit and scope of the invention. For instance, various components may be repositioned as desired. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present invention. Accordingly, the scope of the present invention is intended to be defined only by the claims that follow. 

1. A method of plastically forming splines on a shaft-like workpiece, wherein a volume of splines formed on the shaft-like workpiece is made substantially equal to a volume of a plastically processed portion, the method comprising: preparing the shaft-like workpiece such that the shaft-like workpiece has a maximum diameter in a portion where spline formation will begin, and such that the shaft-like workpiece extends in a conical shape from the portion where spline formation will begin toward a portion that will not be plastically processed; loading the shaft-like workpiece onto a machine and forming the splines.
 2. The method according to claim 1, wherein the splines are plastically formed on the shaft-like workpiece using frequency modulation while a feeder produces relative motion between the shaft-like workpiece and a die.
 3. A shaft-like workpiece blank comprising a shaft portion and a working portion, the working portion comprising a distal end and a proximal end with the proximal end being closer to the shaft portion than the distal end, the working portion being adapted to receive splines by plastic deformation, the working portion comprising a distal outer diameter and a proximal outer diameter, the distal outer diameter being larger than the proximal outer diameter and an outer surface of the working portion tapering from the distal outer diameter to the proximal outer diameter.
 4. The blank of claim 3, wherein the outer surface tapers at an angle of between about 2 degrees and about 3 degrees.
 5. The blank of claim 3, wherein there is no location along the working portion in which a diameter is smaller than a diameter proximal of that location.
 6. The blank of claim 3, wherein there is no inflection point along the tapering outer surface. 